Followers.

Natural stone has been used in the construction of buildings because it was thought that any hard, natural stone would resist the action of wind and ram for centuries. Many natural stones have been used in walling and have been durable for a hundred or more years and are likely to have a comparable life if reasonably maintained.

There have been sorne notable failures of natural stone in walling, due in the main to a poor selection of the materia! and poor workmanship. The best known example of decay in stonework occurred in the fabric of the buses of Parliament, the walls of which were built with a magnesian limestone from Ancaster in Yorkshire.

A Royal Commission reported in 1839 that the magnesian limestone quarried at Bolsover Moor in Yorkshire was considered the most durable stone for the Houses of Parliament. After building work had begun it was discovered that the quarry was unable to supply sufficient large stones for the building and a similar stone from the neighbouring quarry al Anston was chosen as a substitute. The quarrying, cutting and use of the stone was not supervised closely and in consequence rnany inferior stones found their way into the building and many otherwise sound stones were incorrectly laid.

Decay of the fabric has been continuous since the Houses of Parliament were first completed and extensive, costly renewal of stone has been going on for many years. At about the same time that the Houses of Parliarnent were being buili, the Museum of Practical Geology was built in London of Anston stone from the same quarry that supplied the stone for the Houses of Parliament, but the quarrying, cutting and use of the stones was closely supervised for the museum, whose fabric remained sound.

The variability of natural stone that may appear sound and durable, but sorne of which may not weather weIl, is one of the disadvantages of this material which can, when carefully selected and used, be immensely durable and attractive as a walling material.